Given the increasing scarcity of resources and the increased efforts to save energy associated therewith, systems of the above type are becoming increasingly important. Such systems are used in hydraulic devices and systems for example, in which actuators in the form of working cylinders are provided. The working cylinders generate movements against a load as consumers, or generate energy from load forces for storage in the hydraulic accumulator. For example, in lifting and lowering applications, the potential energy of a lifted load can be converted into hydraulic energy, which may be stored and recycled. Hydraulic hybrid systems for rotary drives are a further field of application. In this case, the actuator has a motor pump unit between a drive motor and a working hydraulics or hydrostatic drive. The motor pump unit functions as a consumer or as a generator of hydraulic energy for storage and recycling in the hydraulic accumulator in corresponding operating states.
Regardless of the application, the efficiency of the energy conversion in the known systems leaves something to be desired. One reason for this efficiency issue is the dependence of the charging and discharging processes of the hydraulic accumulator on the respective system pressure. More specifically, the hydraulic accumulator can still only be charged when the system pressure is greater than the gas pressure found in the accumulator on the gas side. When the system pressure cannot be built up in the respective operating situation of the actuator, energy cannot be acquired in the accumulator. The discharge process of the accumulator is subject to the restriction that energy can only be fed back from the accumulator when the accumulator pressure is still greater than the current system pressure. In addition, there is the problem that in the case of an accumulator pressure that is greater than the currently needed system pressure, the pressure levels of the accumulator and the system must be balanced by valves, so that the energy contained in the differential pressure between the accumulator pressure and the system pressure is lost due to throttling losses.